The control of cellular transformation by virus and cell genes is being examined using a) normal rat kidney (NRK) cells transformed by wild type MSV or a cold-sensitive mutant of MSV, b) morphological revertants of MSV-transformed NRK cells and c) human tumor cell lines and chemical carginogen, MSV-transformed or revertant human cells. The goals are a) to identify transforming proteins by immunoprecipitation of metabolically labeled cell extracts with sera from animals bearing tumors induced by MSV-transformed cells, b) to examine cell extracts by one- and two-dimensional gel electrophoresis for alterations in host cell polypeptides that accompany the morphological or growth phenotype of transformation or which may restrict or modify the expression of transforming proteins resulting in reversion of the transformed cell and c) to isolate mutants of MSV temperature-sensitive for growth parameters of transformation.